Zinc Phosphate coating is a crystalline conversion coating that is formed on a metal substrate. The phosphate process relies on the chemical reaction between the metal and the mildly acidic phosphate liquid to form insoluble crystalline phosphates on the surface of the part.

The phosphate coating is used as a pretreatment prior to painting, increasing corrosion protection, and providing for a better adhesion of the coating system.

When phos is used alone or in combination with oil (phos and oil) it lowers friction characteristics of sliding components or threaded parts. While typically called phos coating, phosphate alone has poor rust inhibiting characteristics and must be used in combination with oil or a top coat for corrosion protection. Zinc Phosphate can be applied to Ferric metals, but has no effect on Stainless Steel.